What is the Process of Blow Molding?

Blow moulding is one of the most crucial steps in the manufacturing industries. For example, in the foods and beverage industries, blow moulding is used in the production of plastic bottles and more.


Blow moulding is a process in which air pressure is used to expand a molten plastic in mold cavity. This process is used in the manufacture of hollow plastic or PET parts with thin walls, such as bottles and containers.


Generally, the blow moulding is carried out using a particular machine known as the plastic blowing machine.


Blow moulding is carried out in two steps: first, a tube is made from molten plastic, called a preform, and second, the air is injected into the tube to get the desired shape.


Let’s look at the different forms of blow moulding thus;


Various types of Blow Molding:


Extrusion-Blow molding: The plastic melts and is extruded into a tube (preform) which is closed at the bottom tightly by the mould. Air is injected into the preform to acquire the desired shape. It is then allowed to cool after which the piece is ejected.


Injection-Blow moulding: Injection moulding and blow moulding are combined. The molten plastic is moulded around a core to get a preform. The preform is introduced into the mold; then air is injected to expand the material and get the final shape of the piece. It is then cooled and ejected.


Coextrusion-Blow moulding: this form of PET blow moulding is used basically for the production of multilayer parts. It is a two-stage process similar to injection-blow molding. The process begins with the injection of a preform. The preform is heated with infrared heaters, and high-pressure air is injected while the preform is stretched using a rod. The preform is expanded and adopts the shape of the desired piece.


The Production

Most production and packaging industries produce components by blow moulding with great versatility. During production, such sectors adapt to the needs and guidelines established by each client. In this way, the customer gets the exact mold he needs to make his products.


Rotary stretch blow molding

Materials used in blow moulding

The blow moulding materials are chosen based on their physical properties, cost and the environment in which they will be used. The most used materials and products for blow moulding include the following:

Polyethene terephthalate (PET): It is the most while used material in making bottles.

High-density polyethene (HDPE).

Low-density polyethylene (LDPE or LLDPE).

Polyvinyl chloride (PVC).

Polypropylene (PP).


Products manufactured by blow moulding are widely used in many fields of industry and in daily life, such as automotive, consumer products, electronics, fuel tanks, furniture, health, safety, toys and more.


However, the PET blowing machine price varies and would be dependent on the manufacturer. If you need a blowing machine for your business, it is essential to ensure that your supplier is reliable. You can ask for reviews from previous clients such as friends, family and even sister companies who have dealt with the supplier in the past.